Embodiments of the present invention relate to a fluid flow sensor, which may for example be provided on a downhole tool such as an array flow meter tool.
It is desirable to understand the fluid flow regime in a downhole well which typically includes oil, water and gas. In particular, non-vertical wells may have gases flowing in one direction such as upwards and liquids flowing in another direction, such as downwards, often with differing flow rates.
An example of a fluid flow sensor uses three magnets spaced axially along a long helical rotating turbine or so-called “spinner” which is difficult to rotatably balance. In addition, the sensors used may not be very sensitive and may require strong magnets and/or small clearances between the turbine and the surrounding housing. The magnets also have a tendency to attract magnetic debris causing fouling of the miniature turbine.
It would be desirable to have a fluid flow sensor which overcomes or at least alleviates at least some of the problems of known sensors.